In recent years, an HDMI (High Definition Multimedia Interface) is becoming increasingly popular as a communication interface to transmit a digital video signal, that is, a non-compressed (baseband) video signal (hereinafter, referred to as “image data”) and a digital audio signal (hereinafter, referred to as “audio data”) accompanying the video signal at high speed from, for example, a DVD (Digital Versatile Disc) recorder, set top box, or other AV sources (Audio Visual sources) to a TV receiver, projector, or other displays. For example, WO2002/078336 contains a detailed description of the HDMI standard.